[HUST CSE] Fix: 字符数组str越界

[suywang]

拉取/合并请求描述：(PR description)

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为什么提交这份PR (why to submit this PR)

在board/TencentOS_tiny_EVB_G0/KEIL/mqtt_iot_explorer_tc_pm25/demo/mqtt_iot_explorer_tc_pm25_oled.c这个文件中，第85行创建的字符数组str大小只有16，后续后续101和103行sprintf的字符串明显超出了16的大小，会发生数组越界，出现问题

你的解决方案是什么 (what is your solution)

将str字符数组开大空间，统计了一下最长是26，因此开辟30的空间

在什么测试环境下测试通过 (what is the test environment)

只增加了str的空间，因此测试一定会通过

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[tencent-adm]

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